The fence works. The sheep have reverted to a natural diet and returned to their former range, which at higher elevations ends at the line of dense vegetation: They simply won't go where they can't see mountain lions and other predators.

Glorious as the sheep are, the true stars of California's wilderness may be its plants—from giant sequoias and coastal redwoods to flowers setting meadows ablaze to tiny, brittle plants growing in the region's infertile soils. Rocks from the Earth's mantle seldom see the sunlight. It's only in places where tectonic plates have collided, like California, that mantle rock—loaded with magnesium, iron, nickel, chromium, cobalt, but low in calcium—has been squeezed to the surface. Water changes the rock to serpentinite, named for its green snakeskin pattern, which, as it weathers, breaks down into nutrient-poor soil, heavy with metals. Such soils would kill most plants.

Yet only in the small scattered pockets of serpentine soils will you find Streptanthus breweri, surrounded by rocks glowing in the sun, glassy and metallic. This plant is but a rosette of grayish leaves until the spring, when it sprouts a single stem with tiny purple blossoms, gems that gave it its common name—jewelflower.

S. breweri has other tricks. To defend itself against the caterpillars of a butterfly that lays its eggs on the plant, S. breweri has evolved leaves edged with raised orange dots—fake eggs, designed to fool the butterflies into thinking another butterfly got there first.

"That's what California's biodiversity is all about," says ecologist Susan Harrison. "Small things giving rise to other small things." Harrison works with state agencies and local groups to encourage the setting aside of serpentine-rich lands. In public talks she stresses the rarity of these plants and how, because many are new species, they offer scientists a "natural laboratory of evolution"—a way to investigate how biodiversity comes about.

Much of the state is so distinctive, in fact, that scientists dubbed it (with apologies to Oregon and Mexico, which contribute parcels) the California Floristic Province. With a Mediterranean climate, geology as mixed as fruitcake, and isolation behind the Sierra Nevada to the east, the province yields a remarkable floral abundance. Of its 3,488 native plant species, 60 percent can be found nowhere else on Earth. The count of endemic animals pales by comparison: reptiles, 4 species; birds, 8; freshwater fish, 15; mammals, 18; amphibians, 25. But endemic insect species number in the thousands.